Michael Nelson Denham
1807 – 1871
When adding the 1850 census, the Maines siblings appear on Michael's page. Please correct.
There's nothing wrong with Source Linker. It's just showing the matching profile from the Tree and all of its immediate relatives (parents, spouses, children, and siblings), as it always does. (I checked this on the 1870 census page for the family, which is not yet fully attached: https://www.familysearch.org/search/linker?pal=/ark:/61903/1:1:M4XX-W5J&id=LVDS-DFZ.)
There are multiple mothers entered for Michael Nelson Denham in the Tree: Margaret Cheesman and Margaret Nelson. The latter has another husband attached, an Isaac Maines, and she has 6 children with him. That's where the Maines people in the right-hand (Tree) column of Source Linker are coming from. They're Michael's (half-)siblings.